Examining oral argument in the Australian High Court and comparing to the U.S. Supreme Court, this article shows that institutional design drives judicial interruptive behavior. Many of the same individual- and case-level factors predict oral argument behavior. Notably, despite orthodoxy of the High Court as “apolitical,” ideology strongly predicts interruptions, just as in the United States. Yet, important divergent institutional design features between the two apex courts translate into meaningful behavioral differences, with the greater power of the Chief Justice resulting in differences in interruptions. Finally, gender effects are lower and only identifiable with new methodological techniques we develop and apply.